1. Technical Field
This application relates to calibrating an internal clock generator.
2. Description of Related Art
Various electronic devices require a more or less exact and reliable clock signal. Such clock signals are typically generated by various types of oscillators, which deliver an alternating current (AC) signal on a fixed or tunable frequency. There are certain applications which require an accurate reference frequency. Electronic paper display (EPD) driver and authentication tokes are but two of many such applications. In the case of EPDs, a typical requirement for an EPD driver is a precise 32.768K Hz clock.
Moreover, an increasing number of devices are designed to be operated by battery. These devices may be required to operate for a relatively long time, in some instances for one or more years. Examples of such devices include authentication tokens employing displays such as an LED or electronic paper display. In order to increase battery life, such devices are designed for reduced power consumption.
It is known in the art that high frequency crystal oscillators are generally much more accurate than resistor capacitor (RC) oscillators or internal clock signals generated by semiconductor devices such as a microprocessor. However, high frequency crystal oscillators are more costly, consume additional physical space, and have higher power consumption. For applications with extreme physical restrictions, it is sometimes impossible to include an external quartz crystal due to stringent space restrictions. RC oscillators available in semiconductor devices often have a high variation such that they don't provide the necessary precision.